cheers chaps I will give your idea's a try.
I am thinking its virus related.
Mark
Think you are right, try an internet search on another PC, if you can, and look for any info on a virus that causes a start up loop. 34 years working with PC's and never found a problem similar to that that was due to faulty ram or a dodgy motherboard, no disrespect to the techies on here. 99.9% of the time it is caused by a virus in my experience. Or you could try this as suggested by others:
* Set your first boot device in the Bios to CD-Rom. Insert your Windows XP/Vista/Windows 7 CD, save the bios settings and exit. Soon "Press any key to boot of CD" will appear on the screen, hit the space bar to continue.
* Now setup will inspect your hardware and software, it then will load various files required for the repair. Just wait and be patient, this may take a few moments.
* Soon a menu will appear (as pictured below), press enter to continue.
* Now the "End User Agreement" Press "F8" if you agree, "ESC" if you don't.
* You will now have to select the installation you wish to repair. Usually there is only one, but sometimes, there may be 2 or more (i.e. you have done a parallel install to resolve a problem), use the up/down arrow key to select the install, and then press "R" to continue.
* Setup will now examine the disk be patient, it can take a few minutes.
* Setup will go through a percentage - 1 to 100%
* A screen will soon appear. Press "F3" to continue
* Now setup will reboot system, wait 15 seconds or just press enter.
* Now it is time to see if this has solved your problems.